The present invention relates to a control method for a multi-stage hydraulic machine having a plurality of stages from the highest-pressure stage to the lowest-pressure stage, and more particularly to a control method for a multi-stage hydraulic machine in which the runner chambers of adjacent stages communicate with each other through a return channel and at lowest-pressure stage is provided with movable wicket gates, the control method being applicable to the period of time during which the mode of operation is shifted from the idling operation to the power generating operation or the pumping operation.
In single-stage hydraulic machines used in pumped storage power plants, highly pressurized air is in general fed by a water level depressor to a point above the water level at the upper part of a suction pipe in order to reduce the torque for driving a runner during the turbine condenser operation or the pump starting operation. The air thus fed causes the water level to go down so that the runner is operated in the air. Thereafter, the air fed into the channel path is exhausted and the water level goes up and then the flow path is filled with water. In this manner, the hydraulic machine is changed in mode of operation to a predetermined turbine generating or pumping operation.
In a multi-stage hydraulic machine having a plurality of stages, the runner chambers of adjacent stages communicate with each other through a return channel. Therefore, the multi-stage hydraulic machine has a complicated channel system. Thus, various difficulties are found in the air exhausting operation when the idling operation is shifted to the power generating operation or the pumping operation.
Particularly in the case of a multi-stage hydraulic machine provided with movable wicket gates in the highest-pressure stage in order to safely control the driven condition during this transition, the channels of the respective stages from the highest-pressure stage to the lowest-pressure stage are in constant communication with each other. Consequently, when the air remaining in the channels is exhausted, mutual interference occurs among the respective stages. Thus, it is difficult to carry out smoothly the air-exhausting/water-filling operation and there arises a problem of exhaustion of the residual water.
Multi-stage hydraulic machines provided with movable wicket gates in their highest-pressure stage have not been extensively developed from the technical point of view. In fact, no convenient and proper control method for such machine has been yet proposed that is applicable in the case where the idling operation is changed to a predetermined power generating or pumping operation.